The present invention relates to a communication method to be used in a communication network comprising a buffering element, a line termination element and a plurality of network termination elements, wherein the buffering element is coupled to the line termination element, and the line termination element is coupled to each of the network termination elements over a shared medium.
Such a communication method is already known in the art, e.g., from “TCP/IP friendly APON MAC with traffic regulator” from the authors K. Venken et al. This article is published in Proceedings of the 17th World Telecommunications Congress, WTC/ISS2000, 7-12 May 2000, Birmingham.
Therein, a shared medium access network is described. The main function of such a shared-medium access network is to collect and multiplex traffic from several users and offer it to the core network and additionally to distribute the traffic from the core network to the relevant users. This involves the multiplexing and de-multiplexing of several connections. Typically, the access network has a point to multi-point topology where all traffic between the Network Terminations called the Optical Network Unit in the cited article and the core network flows through the line termination called the optical line termination of the access network in the cited article. Cells are broadcast in the downstream direction from line termination towards the Network Terminations. Multiple network terminations share the upstream direction as well as in the downstream direction. Therefore, a Medium Access Control further referred to as MAC function is needed for controlling the upstream channel. Centrally controlled request-based MAC protocols for Time Division Multiple Access transport systems are very well known. One time-slot corresponds with one cell. Different timeslots are dynamically assigned to different network terminations, under control of the MAC function implemented at the line termination.
The allocation of time-slots is based on the traffic parameters, i.e., connection set-up information, and the Quality of Service requirements of the connections. Dynamic bandwidth allocation also takes into account the instantaneous traffic-needs of the connections, e.g., the number of waiting cells at the network terminations. The MAC-channel consists of the requests of the network terminations sent to the line termination and the permits broadcast from line termination to the network terminations.
Additionally, it is well known in the art that the core network contains network elements, as described in “A versatile RED based Buffer Management Mechanism for the efficient Support of Internet Traffic” from the authors J. Nelissen and S. De Cnodder and published in November 1999 in Proc. SPIE Vol. 3842, p. 57-68, Internet II: Quality of service and future directions by R. O. Onvural et al. having limited buffering capabilities together with buffer acceptance capabilities, meaning that these network elements discard and/or mark incoming cells based on the filling degree of such a buffering element.
As a consequence, in case cells are discarded by such a buffering element in the core network, the sending of this same discarded cell over the shared medium between the network terminations, and the line termination was superfluous in the meaning that instead a competing cell not to be discarded could have been sent.